1. Field of the Invention
The present invention relates to a tenter frame construction, and more particularly, pertains to a novel tenter frame clip which is at least partially constituted from a lightweight polymeric composite material.
In essence, clips which are employed in tenter frames as components of clip-chain assemblies for grippingly engaging and advancing thermoplastic film webs, fabrics or foils through the tenter frame as the web is concurrently transversely stretched, are generally constituted from either cast iron or cast steel, depending upon the type and size of tenter frame may each readily weigh as much as five pounds, and even higher. The clips are usually extremely strong and tough in their construction and are each able to exert a gripping force of up to 1500 to 2500.
Inasmuch as each tenter frame may incorporate hundreds of such clips, and possibly at times even thousands of clips, and their ancillary equipment, it becomes readily evident that the overall weight which is represented by the multiplicity of clips is quite considerable, and necessitates an extensive amount of electric power and heavy drive units, such as motors and the like, for a tenter frame drive. Similarly, the utilization of a large quantity of such heavy clips, which generate considerable frictional forces when slidingly contacting support rails on the tenter frames, necessitates the installation of either wear strips on the surfaces of the supporting rails along which the clips are conducted and with which they come into sliding contact, or the need for the constant or frequent application of large amounts of liquid lubricants, oils or grease between the contacting sliding surfaces, to thereby reduce friction to tenable levels.
In order to reduce the weights of such clips, thereby resulting in an overall reduction in the weight of the movable constituents of a tenter frame installation, so as to thereby lower the electric power consumption for the operation thereof, and possibly allow for the utilization of smaller-sized drive motors and components, with attendant savings in material and costs, it may be expedient, pursuant to the present invention, to construct at least parts of each of the clips from a lightweight polymeric composite material possessing a high level of strength, toughness and thermal stability generally commensurate with the properties evidenced by the heavier-weight cast iron or cast steel constructions.
2. Discussion of the Prior Art
In essence, although numerous types of tenter frame clip constructions are presently known and employed in this technology, none of these contemplate the use of relatively lightweight polymeric materials with regard to the clip structures.
Lechner U.S. Pat. No. 4,658,482 discloses a tenter frame clip which is designed to incorporate various plastic components; however, these are primarily for the purpose of contacting metallic rail surfaces so as to attenuate or dampen the level of vibration which is encountered during operation, so as to increase service life and reduce noise levels.
Similarly, Ida, et al. U.S. Pat. No. 3,789,975 discloses a tenter frame clip unit having a resilient plate member but does not pertain to the utilization of a lightweight polymeric material in this construction in order to provide for savings in weight.
Takasaki U.S. Pat. No. 3,789,468 discloses a tenter clip for tenter frames, wherein the clip grippingly engages a thermoplastic film web and which conceivably may incorporate plastic components. However, there is no specific reference to the use or installation of such materials.
Finally, Dornier, et al. U.S. Pat. No. 3,638,289 discloses a tenter frame assembly including a clip unit which is adapted to slidingly contact various frame components, but does not provide for utilization of a polymeric material to reduce the overall weight of the installation.